One of my ubuntu machines, a netbook running Gnome classic on Ubuntu 12.04 (32bit), has a problem: I cannot resize windows. I can unmaximize them and remaximize them, and the resize icons do appear when I place the mouse pointer on the edges, but I cannot grab and resize those edges.

I have googled around and found people with problems like borders being too thin and hard to grab -- this is not the case here. It is also not application specific -- I cannot resize any windows.

What should I look at and fix? I am a developer and can get around a terminal without destroying things fine. I just don't know where to start.